python学习笔记（七）之列表

列表：是一个加强版的数组，什么东西都可以往里面放。

创建列表

创建一个普通列表：

1 >>> member = ['operating system', 'data structure', 'network', 'principle of computer composition']
2 >>> member
3 ['operating system', 'data structure', 'network', 'principle of computer composition']

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创建一个混合列表：

1 >>> mix = [1, 'hello python', 3.14159, [1,2,3,['one','two']]]
2 >>> mix
3 [1, 'hello python', 3.14159, [1, 2, 3, ['one', 'two']]]

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创建一个空列表：

1 >>> empty = []
2 >>> empty
3 []

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向列表中添加元素

使用append()，extend(),和insert()方法

append()在尾部添加，extend()用一个列表来扩展列表，insert(index, obj)在index处插值。

1 >>> member.append('mechine learning')
2 >>> member
3 ['operating system', 'data structure', 'network', 'principle of computer composition', 'mechine learning']
4 >>> member.extend(['data mining', 'hadoop'])
5 >>> member
6 ['operating system', 'data structure', 'network', 'principle of computer composition', 'mechine learning', 'data mining', 'hadoop']
7 >>> member.insert(0,'PE')
8 >>> member
9 ['PE', 'operating system', 'data structure', 'network', 'principle of computer composition', 'mechine learning', 'data mining', 'hadoop']

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从列表中获取元素

和数组一样，通过元素的索引从列表中获得单个元素，索引从0开始。

 1 >>> for i in range(len(member)):
 2 ...     print(member[i])
 3 ... 
 4 PE
 5 operating system
 6 data structure
 7 network
 8 principle of computer composition
 9 mechine learning
10 data mining
11 hadoop

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通过列表分片

1 >>> member[3]
2 'network'
3 >>> member[:3]
4 ['PE', 'operating system', 'data structure']
5 >>> member[3:]
6 ['network', 'principle of computer composition', 'mechine learning', 'data mining', 'hadoop']
7 >>> member[3:5]
8 ['network', 'principle of computer composition']

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从列表中删除元素

使用remove(),pop()方法或del

 1 >>> member
 2 ['PE', 'operating system', 'data structure', 'network', 'principle of computer composition', 'mechine learning', 'data mining', 'hadoop']
 3 >>> member.remove('hadoop')
 4 >>> member
 5 ['PE', 'operating system', 'data structure', 'network', 'principle of computer composition', 'mechine learning', 'data mining']
 6 >>> member.pop()
 7 'data mining'
 8 >>> member
 9 ['PE', 'operating system', 'data structure', 'network', 'principle of computer composition', 'mechine learning']
10 >>> member.pop(2)
11 'data structure'
12 >>> member
13 ['PE', 'operating system', 'network', 'principle of computer composition', 'mechine learning']
14 >>> del member[3]
15 >>> member
16 ['PE', 'operating system', 'network', 'mechine learning']
17 >>> del member
18 >>> member
19 Traceback (most recent call last):
20   File "<stdin>", line 1, in <module>
21 NameError: name 'member' is not defined

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列表的一些常用操作符

　　比较操作符 >， >=， < ，<=， == ，!=

1 >>> list1 = [123]
2 >>> list2 = [456]
3 >>> list1 < list2
4 True
5 >>> list1 = [123,456]
6 >>> list2 = [234,123]
7 >>> list1 > list2
8 False

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　　逻辑操作符 and， or， not

1 >>> list3 = [123,456]
2 >>> list1 < list2 and list1 == list3
3 True
4 >>> list1 > list2 or list1 < list2
5 True
6 >>> not list1 < list2
7 False

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　　拼接操作符 *

1 >>> list4 = list2 + list3
2 >>> list4
3 [234, 123, 123, 456]

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　　重复操作符 *

1 >>> list4
2 [234, 123, 123, 456]
3 >>> list4 * 5
4 [234, 123, 123, 456, 234, 123, 123, 456, 234, 123, 123, 456, 234, 123, 123, 456, 234, 123, 123, 456]

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　　成员关系操作符in， not in

1 >>> 123 in list4
2 True
3 >>> 345 in list4
4 False
5 >>> 345 not in list4
6 True

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列表一些常用的方法

　　count():返回列表内某个成员出现次数，如果不存在则返回0

1 >>> list4
2 [234, 123, 123, 456]
3 >>> list4.count(123)
4 2

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　　index()：返回该元素在列表第一次出现位置的索引，若不存在，则抛出一个ValueError异常。

1 >>> list4.index(123)
2 1
3 >>> list4.index(124)
4 Traceback (most recent call last):
5   File "<stdin>", line 1, in <module>
6 ValueError: 124 is not in list

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　　reverse():翻转列表

1 >>> list4
2 [456, 123, 123, 234]
3 >>> list4.reverse()
4 >>> list4
5 [234, 123, 123, 456]

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